1. Field of the Invention
The present invention relates to a keypad structure, and particularly to a thin-type keycap structure and a keypad structure including such keycap structure and a method of making such keycap structure.
2. Description of the Prior Art
Due to the development of electronic technology, the demand for keypads is dramatically increasing. The keypads used in calculators, mobile phones and the like further have to be relatively thin and small for the device with reduced size and weight as desired.
A thin-type keycap is conventionally formed by molding. As shown in FIG. 1, a film 2 is compressed and drawn in a mold 4 in order to have bulged portions 6 each in a keycap shape. There is a hollowed recession 8 beneath each bulged portion 6. Thereafter, a resin 9, such as UV curable resin, is injected into each recession 8 by an injection machine and cured. The injection temperature is usually higher than 200° C.
It is known that the molding of the film 2 in the mold 4 can be performed by hot press through a male mold and a female mold. In such process, a printing layer of characters and graphs is printed on the bottom surface of the film 2 in advance. When the film 2 is hot pressed to gain the keycap contour using the male mold and the female mold, the ink of the printing layer, especially at corners of the keycap contour, may be thinned out or broken, due to the stretching and deformation of the film 2. It will decrease the product yield. Alternatively, it is known that the film 2 is molded through pressing the film 2 tightly on a bottom mold in accordance with the profile of the bottom mold by vacuum, so as to impart the mold profile to the film 2. However, the vacuum process is time-consuming and costly.
Furthermore, conventionally, if it is desired that the outer surface of the film 2 has a pattern, the pattern is often formed by placing an additional pattern layer thereon. In this way, the thickness is undesirable increased and the fabrication is more complicated.
Therefore, there is still a need for a novel keycap structure and a method of making the same for making keypads economically and conveniently.